Analysis of key warning points and environmental conditions for the '4.04'strong downburst event in Hengyang of Hunan

Abstract

On the afternoon of 4 April, 2023, an intense downburst event (referred to as the '4.04' strong downburst) occurred in Hengyang, Hunan, causing serious disasters. This study analyzes the key warning indicators and environmental conditions for extreme strong winds using conventional meteorological observations, Doppler weather radar, and NCEP 1°×1° reanalysis data. The results are as follows: (1) The '4.04' strong downburst occurred under a 'baroclinic frontogenesis' weather system configuration, with a surface cold front providing the triggering conditions. The Skew-T plots clearly showed characteristics of high-level dryness and low-level moisture, unstable atmospheric convective parameters, and corrected convective available potential energy (CAPE), along with strong vertical wind shear, all conducive to the occurrence of extreme strong winds. (2) A mesoscale convective system (MCS) with bow echoes swept through Hengyang, causing regional downbursts. Extreme strong winds occurred when the corresponding storm cells moved rapidly, with maximum reflectivity factors reaching 60 dBz. The vertical integrated liquid water content and centroid height rapidly decreased. The reflectivity factors displayed a noticeable tilted structure, with clear features of bow echoes, rear-inflow jets, and radial velocity ambiguity. The low elevation asymmetric high-speed regions and velocity convergence are key warning indicators for extreme strong winds. (3) The strong downburst exhibited significant convective potential, with strong low-level moisture flux convergence and high specific humidity. There were conditions of thermal instability and vertical upward motion, along with low-level convergence and upper-level divergence. Cold air played an important role in the occurrence and development of this downburst event.

Keywords

• downburst
• asymmetric high-speed
• rear-inflow jet
• bow echo